Four wildlife advocacy groups filed suit Tuesday against the U.S. Fish and Wildlife Service, seeking to put the predator back on the federal endangered species list less than a year after it was removed.

Actions by Minnesota and Wisconsin -- including the wolf hunts that began last year -- are central to the suit's argument, which asserts that the wolf is not being adequately protected and that its continued survival is in jeopardy.

Placing responsibility for the wolf's survival in the hands of state governments "paves the way for the same state-sponsored eradication policies that pushed this species to the brink of extinction in the first place," said Jonathan Lovvorn, senior vice president at the Humane Society of the United States.

The suit was filed by the Humane Society, Born Free, and two Minnesota organizations, HOWL and FATE.

Officials from the U.S. Fish and Wildlife Service and the Minnesota Department of Natural Resources (DNR) declined to comment on the suit, which had been expected since October, when the Humane Society notified the agency of its intent to challenge the de-listing.

The suit says that already hundreds of wolves have been shot and trapped, and that Wisconsin allows dogs, snares, night hunting and leg-hold traps. Minnesota, it says, failed to implement a five-year hunting moratorium that was part of its wolf-management plan. State wildlife officials have said that it took so long for the wolf to be de-listed after the management plan was crafted that the moratorium wasn't necessary.

State officials have also said that Minnesota's first-year quota of 400 animals is not enough to threaten the population, because wolves can easily replace that number through reproduction.

The federal suit is now the second legal fight underway over Minnesota's wolves. Last year another wildlife advocacy group, the Center for Biodiversity, filed suit in the Minnesota Court of Appeals claiming that the DNR violated its own rules by not giving the public adequate chances to weigh in on the state's hunting plan. The DNR has said that the public had plenty of opportunity to comment during the legislative process that established the hunt last year.

That case is scheduled for oral arguments in early April.

Now, some officials fear, the decade-long legal wrangling over the wolf may pose a threat to the Endangered Species Act itself. The wolf was de-listed in western states by a new federal law that, in effect, bypassed the act. And state legislators have raised questions about the act and the litigation it has generated over the wolf's status.

The Wisconsin Assembly planned to finish its work for the year Thursday by approving $350 million to build a new prison and provide all parents a $100 per-child tax rebate, although it's uncertain whether either will pass the Senate.

A couple hundred Minneapolis students set out Wednesday afternoon on a march from Martin Luther King Jr. Park in south Minneapolis to City Hall to "voice our concerns about gun violence in schools," according to a Facebook post.